Not long ago Sony released a optical low pass filter for the F5/55 called the CBK-55F2K. This is a user changeable filter and can be installed in a matter of minutes by replacing the existing filter that sits in front of the sensor. The OLPF can be swapped back and forth and is not designed as a permanent replacement for the existing filter. So why would you need a OLPF? Here is a little insert from Alister Chapman over at xdcam-user.com. Alister is in my opinion THE go to guy for any sort of technical or user operation questions when it comes to Sony cameras.

Alister wrote:

Sony’s FS700, F5 and F55 cameras all have 4K sensors. They also have the ability to shoot 4K raw as well as 2K raw when using Sony’s R5 raw recorder. The FS700 will also be able to shoot 2K raw to the Convergent Design Odyssey. At 4K these cameras have near zero aliasing, at 2K there is the risk of seeing noticeable amounts of aliasing.

One key concept to understand from the outset is that when you are working with raw the signal out of the camera comes more or less directly from the sensor. When shooting non raw then the output is derived from the full sensor plus a lot of extra very complex signal processing.

Aliasing shows up in images in different ways. One common effect is a rainbow of colours across a fine repeating pattern, this is called moiré. Another artefact could be lines and edges that are just a little off horizontal or vertical appearing to have stepped or jagged edges, sometimes referred to as “jaggies”.

Now Sony themselves aren't really marketing the CBK-55F2K as an anti moire or anti aliasing filter. They are saying that "The CBK-55F2K will result in "softer, more organic" imagery when shooting in 4K. When shooting HFR in 2K RAW the new filter will result in more pleasing imagery."

So is this a real problem Sony are addressing or is it just another tool for you to create a different look with your camera? I was interested to see for myself. Before I get into what I found I must first say that I haven't really seen any bad moire or aliasing when shoot 2K in HFR or when shooting 4K. I'm sure there is some there but the camera just doesn't have the moire or aliasing we used to see on DSLRs. I remember how horrible my 7D used to look in 720p 50p.

I got the filter in Japan and at close to $900 it is not cheap! It is a tiny component and looks very fragile. A word of warning be very careful when handling this filter and installing it as you can easily get dust or scratch marks on it. When installing it be in the mindset that you are a brain surgeon and any small slip could be fatal! This maybe sounds a bit melo dramatic as it really isn't that difficult to change but still be very careful. You unscrew one tiny screw and slide the filter gently to the right. You then put the CBK-55F2K filter in by sliding the filter to the left and then carefully screwing it back in.

I took my F55 down to the beach after installing the filter and filmed some high speed material in 2K raw to the Sony R5 recorder. My first impressions were that it softens the image quite dramatically. Now this may produce a more organic looking image as Sony touts but the flip side was I found it very hard to focus. Even with the peaking on and using the OLED EVF I really struggled. I had previously been shooting down at my favourite spots a day earlier without the CBK-55F2K fitted. I had also shot 2K raw at HFR as well as 4K raw. I didn't see any moire or aliasing in anything I shot.

I did do some normal moire and aliasing tests by shooting fine lines and patterned clothing etc. and found there to be a small amount on the F55 when shooting HFR in 2K raw. There was also a very small amount in 4K raw but it is barely visible. When I switched in the CBK-55F2K filter I did notice a difference so it definitely does work. The difference is there but it is not always obvious. I'm not a pixel peeper so if I don't see a problem it doesn't mean it is not there. I am gong on my 24 years of being a cameraman and judging on what I see with my own eyes. The thing is how many times are you going to be shooting in situations where you may see aliasing or moire? For me personally it is not a lot and as I said before I have never noticed a problem.

As far as the "More organic look" goes it does have some merits. I found the F55 produces really nice imagery when coupled with the R5 raw recorder. The CBK-55F2K does take that image and soften it up even more and it does look quite nice. It is very easily sharpened up in post can see myself using it for certain situations or shoots, but I didn't find it to be a piece of equipment that you absolutely had to use if you wanted to shoot 2K raw at HFR or 4K raw.

For FS700 as far as i'm aware there is no plans at this stage for a similar filter.

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